Energy storage devices such as ultracapacitors, also known as electrochemical double layer capacitors (EDLCs), may be used in many applications where a discrete power pulse is required. Example applications range from cell phones to hybrid vehicles. Energy storage devices typically comprise a porous separator and/or an organic electrolyte sandwiched between a pair of carbon electrodes. The energy storage is achieved by separating and storing electrical charge in the electrochemical double layer at the interfaces between the electrolyte and the electrodes. Important characteristics of these devices are the energy density and power density that they can provide, which are both largely determined by the properties of the carbon based electrodes.
Carbon-based electrodes suitable for incorporation into high energy density devices are known. The carbon materials, which form the basis of such electrodes, can be made from natural or synthetic precursor materials. Known natural precursor materials include coals, nut shells, and biomass, while synthetic precursor materials typically include phenolic resins. With both natural and synthetic precursors, carbon materials can be formed by carbonizing the precursor and then activating the resulting carbon. The activation can comprise physical (e.g., steam) or chemical activation.
A property of the carbon that can influence its success when incorporated into high energy density devices such as EDLCs is the material's specific capacitance. Higher volumetric specific capacitance generally results in a higher volumetric energy density of the resulting device. Accordingly, it would be an advantage to provide activated carbon materials having a high specific capacitance. Such materials can be used to form carbon-based electrodes that enable higher energy density devices.